High voltage circuit breaker with pressurized breaking chamber of low liquid type

ABSTRACT

An arrangement for preventing high voltage liquid minimum circuit breakers from restriking when breaking capacitive loans. The liquid in the breaking chambers is put under high pressure by supplying compressed gas through an insulating conduit from earth potential to a space above the liquid level in each chamber. Between the gas-filled space and the conduit is a valve, which is open during normal operation but closes during a breaking operation, thus preventing carbonized liquid from penetrating into the conduit.

United States Patent inventors Walter Pucher;

lnge Gard; Karl Cote Persson, all of Ludvllta, Sweden Appl. No. 787,179 Filed Dec. 26, 1968 Patented July13,1971 Assignee Allmanna Svenska Elektriske Aktiebolaget Vasteres, Sweden Priority Dec. 27,1967

Switzerland 17790/67 HIGH VOLTAGE CIRCUIT BREAKER WITH PRESSURIZED BREAKING CHAMBER or LOW LIQUID TYPE 9 Claims, 2 Drawing Figs.

US. Cl 200/150, 200/ 148 R int. Cl H0111 33/68 Field of Search 208/150 B,

[56] References Cited UNITED STATES PATENTS 3,110,783 11/1963 Strom et a1. 200/82 (.1) 3,300,610 l/1967 Roth eta]. ZOO/150 FQRElGN PATENTS 1,537,673 7/1968 France 200/150 B 1,075,706 2/1960 Germany...................... ZOO/150.1 609,589 10/1948 Great Britain 200/ 148.7 918,861 2/1963 Great Britain 200/1500 Primary Examiner-Robert S. Macon Atmrney.lennings Bailey, .1 r.

ABSTRACT: An arrangement for preventing high voltage liquid minimum circuit breakers from restriking when breaking capacitive loans. The liquid in the breaking chambers is put under high pressure by supplying compressed gas through an insulating conduit from earth potential to a space above the liquid level in each chamber. Between the gas-filled space and the conduit is a valve, which is open during normal operation but closes during a breaking operation, thus preventing carbonized liquid from penetrating into the conduitv PATENTEU JUL 1 3 l9?! N s w mFDR THEE zw I VIN N T [R GG N 'L M R A K V! B HIGH VOLTAGE CIRCUIT BREAKER WITH PRESSURIZED BREAKING CHAMBER OF LOW LIQUID TYPE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage circuit breaker of liquid-minimum type, particularly an oil-minimum circuit breaker, and the object of the invention is to provide a circuit breaker of said type which does not reignite even at relatively high operating voltages in the order of lOO kilovolts.

2. The Prior Art The problem of reignition in high voltage circuit breakers is particularly troublesome when breaking capacitive loads, for example breaking capacitors, unloaded overhead lines or cables. When the circuit breaker opens the current is usually broken at the first current zero, after which the capacitance is charged with a direct voltage which is equal to the maximum value of the alternating voltage before the breaking. n the station side of the circuit breaker the voltage'alters with the operating frequency and reaches it maximum value after a half period, this value now having opposite polarity in relation to the direct voltage of the transmission line. If the circuit breaker does not effect the necessary insulation between the breaking contacts sufficiently rapidly, a reignition takes place during this half period so that the capacitance is charged to a higher voltage than the initial voltage, but having opposite polarity. After several successive reignitions the voltage may be built up to such a high value that damages occur in the network. ln most oil circuit breaker constructions the pressure generated by the arc gases is used to extinguish the arc. If, however, the breaking current is low, as is the case for example when breaking an unloaded overhead line, the pressure increase will be breaking to effect any noticeable oil flow in the arc channel. This may cause repeated reignitions in the breaking path resulting in high over voltages. With a view to decreasing the risk of such reignitions when breaking low currents it is known to place the breaking chambers under permanent pressure, for example with the help of compressed gas. In this way an effective liquid flow can be effected past the breaking gap even when the breaking current is relatively low. Most breakers constructed according to this principle, however, have been designed so that the supply of compressed gas to the breaking chamber and the removal of the breaking gas produced during the breaking has been attended to through spaces or channels in the breaking chamber which are separated from each other. This has complicated the chamber and made it relatively space-consuming. Also, the supply of compressed gas in such circuit breakers has been absolutely necessary for the circuit breaker to function at all breaking currents. This means that circuit breakers of this type are completely unusable for compressor faults or when there is a leakage in the compressed gas system.

SUMMARY OF THE INVENTION The high voltage circuit breaker according to the invention comprises at least one contact point arranged in a breaking chamber only partly filled with liquid so that a gas-filled space is formed in the chamber, the space communicating through an insulating conduit with a compressed gas source. However, the aim of placing the breaking chamber under pressure in this case is not primarily to effect a liquid flow in the breaking chamber which is independent of the arc, as is the case in previously known breakers. lt is principally based on the fact that the pressure increase causes a considerable increase in the voltage strength in the oil. Since the oil which flows to the contact point when the current passes zero has high voltage strength, the tendency to reignite in the breaking path upon capacitive breaking decreases considerably. In a circuit breaker of this type it is also possible to simplify the breaking chamber by permitting the supply of compressed gas and removal of exhaust gases to take place in the same space. It

has, however, proved difficult to arrange the supply of compressed gas in a manner satisfactory from all points of view. During a breaking the oil in the breaking chamber moves with considerable force, and, if the compressed gas is supplied to the chamber through a permanently open conduit, oil and breaking gases might penetrate into the conduit. After drying the carbonized oil may leave a coating on the inside of the conduit which causes considerable deterioration of the breaker insulation. This is avoided with the high voltage circuit breaker according to the present invention, which is characterized in that between the gas-filled space in the breaking chamber and the insulating conduit is a valve, in the following called the feeding valve, which is open during normal operation but arranged to close during a breaking process when the pressure in said space exceeds a certain value. By

designing a liquid-minimum circuit breaker in this way,

without extra costs the circuit breaker can easily be prevented from reigniting when breaking capacitive loads at relatively high operating voltages. No specially designed extinguishing chamber is required, but a conventional extinguishing chamber, for example a so-called contraction chamber, can be used to extinguish the arc. In such an extinguishing chamber which is arranged inside the above-mentioned breaking chamber, the breaking is effected with the help of liquid flow generated by the arc. From the operating point of view this has the important advantage that the breaking capacity of the breaker in other respects, for example, its short-circuit breaking capacity, is not dependent on the compressed gas, but remains unaltered even if the compressed gas should disappear. Since not all high voltage circuit breakers need to be constructed for breaking of capacitive loads, the proposed arrangement also has the advantage that the compressed gas system and its valves can be made as additional equipment for a conventional liquid-minimum circuit breaker and only installed when the circuit breaker is to be connected where breaking of capacitive current may rise. in certain cases this may result in considerable savings in costs.

A circuit breaker according to the invention may with advantage be arranged having several series-connected breaking chambers per pole (multiple breaker), in which case a feeding valve of the type mentioned above is arranged in connection with each chamber so that during normal operation there is always full communication between the gas pockets in the chambers and the supply conduit. Pressure equalization is thus achieved in the system and, if full oil communication exists between the chambers, the oil level in these will thus be the same. When the breaking takes place, the valves close so that carbonized oil cannot be blown into the feeding conduits.

Each breaking chamber should suitable be provided with an exhaust valve arranged in connection with the gas-filled space and arranged to open when the pressure in the chamber exceeds a certain limit valve, upon which the exhaust gases are led away to the open air. In order to ensure that the compressed gas communicates freely with the breaking chambers and connection conduit after a breaking the opening pressure of the feeding valve should be higher than the closing pressure of the exhaust valve. lf this were not the case there would be a risk of different pressures prevailing in different chambers due to spreading in the closing pressure of the exhaust valves.

The breaking chamber may, for example, consist of an oblong, hollow porcelain insulator which is arranged with a vertical longitudinal axis, in which case the movable contact of the contact point is arranged to be moved downwardly when the breaker opens. Among other things, this arrangement has the advantage that the movable contact, together with the necessary sliding or rolling contacts, may be entirely in oil, which improves the cooling of these contact members and thus enables the contacts to be of smaller dimensions. Furthermore, the arrangement of the breaker operating mechanism becomes simplified when this can be done from the lower side of the breaking chamber. Thus, for example, with the help of a single operating insulator it is possible to easily operate two contact points from earth potential, the associated breaking chambers then being suitably arranged in V form.

The compressed gas connection to the gas-filled space which with an upwardly directed breaking chamber is suitably situated in the upper part of the breaking chamber thus most easily and cheaply consists of an insulating conduit of, for example, plastic inserted in the breaking chamber. In certain cases, and particularly if the compressed gas system is to be introduces as an addition to an existing circuit breaker, it may be more advantageous if the connection consists of an outer porcelain conduit.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described further with reference to one embodiment shown by way of example in the accompanying drawings. FIG. 1 shows partly in section a minimum oil circuit breaker according to the invention. FIG. 2 shows on a larger scale a feeding valve in the circuit breaker.

The oil-minimumcircuit breaker shown in FIG. 1 consists of two series-connected contact points housed 'each in its own breaking chamber 1 and 2 arranged in relation to each other in V form on a common mechanism housing 3. The connecting terminals of the circuit breaker are designated 4 and 5. The mechanism housing 3 is supported by a hollow supporting insulator 6 mounted on a bottom stand 7. On the same bottom stand is an operating insulator 8 for the circuit breaker.

The breaking chambers l and 2, of which the chamber 2 is shown in cross section, are exactly alike. The breaking chamber 2 consists of a hollow porcelain insulator 9 with a metallic lid 10. inside the breaking chamber 2 is an extinguishing chamber 11 which may, for example, be a differential piston chamber of conventional type. The extinguishing chamber ll contains the stationary contact of the contact point, which is in connection with the connecting member 5. The movable contact 12 of the contact point consists of a solid contact plug which is joined to the operating insulator 8 by means of a link mechanism, not shown. The current transmission between the movable contact 12 and the mechanism housing 3 takes place through a roller contact member 13. The breaking chambers l and 2 are partly filled with oil and the oil spaces in the two chambers communicate to a certain extent with each other through the mechanism housing 3 which is completely tilled with oil so that no seals are required around the movable contacts at their passage between breaking chamber and mechanism housing.

In order to increase the voltage strength in the oil and thus obtain an oil minimum circuit breaker which does not reignite at capacitive breaking, dry compressed gas of a pressure of a few atmospheres is led up to the space 14 on the upper side of the oil volume in each breaking chamber. The compressed gas is generated in a compressor 15 at earth potential which.

should be able to feed several poles or breakers since the compressed gas consumption is low. In order to reduce as far as possible the moisture content of the compressed gas, this should be generated at a pressure at least twice that which shall prevail above the oil surface in the breaking chambers. The compressed gas is led from the compressor 15 to a drying means 16 before reaching the breaking pole through a storage tank 17 and a reducing valve 18. A conduit 19 leads to the other breaking poles and circuit breakers. The compressed gas is led from earth potential through the hollow support insulator 6 up to the mechanism housing 3. From the mechanism housing 3 and up to the space 14 above the oil surface in the lid the compressed gas is led through an insulating conduit 20 inserted in the breaking chamber which may, for example, be made of plastic material, possibly with glass fiber reinforcement. Instead of arranging the compressed gas feeding as shown, it may in certain cases be more suitable to use separate outer porcelain tubes or the like. At the upper opening of the insulating tube 20 is a pressure-sensitive feeding valve 21 which is open if the pressure in the gas-filled space 14 is lower than or equal to the operating pressure, but which closes at an over-pressure and remains closed until the pressure in the chamber decreases to a predetermined value. An exhaust valve is arranged in connection with the gas-filled space 14 which valve 22 is closed at pressures below a certain limit value somewhat above the operating pressure and which opens at pressures above said limit value.

FIG. 2 shows the feeding valve 21 in cross section. The valve consists of a valve housing 23 in which is arranged a piston 24 which is pressed by a spring 25 against a stop in the housing 23. A channel 26 is arranged in the wall of the valve housing. In normal operation the feeding conduit 20 is in free communication with the gas-filled space 14 through this channel 26 and a groove 27 arranged in the piston 24. v

In normal operation the compressed gas in the gas-filled spaces in the chambers l and 2 communicates freely with the supply conduit 20 and since there is also oil communication between the two chambers, the oil level in the chambers will be equal. During a breaking process the openings of the feeding conduits are closed by the pressure-sensitive valves 21, thus preventing the oil and breaking gases from penetrating down into the feeding tubes 20 and thus causing deterioration of the insulation of the breaker. When the pressure in the chambers has exceeded a certain limit value, the exhaust valves 22 open and the exhaust gases are led away to the open air. When the pressure then decreases the valves 21 of the feeding tubes open again briefly before the exhaust valves 22 close so that complete pressure equalization is achieved.

We claim:

1. High voltage circuit breaker of liquid minimum type comprising a compressed gas source at earth potential, a plurality of breaking chambers which are only partly filled with liquid so that a gas-filled space is formed in each chamber, seriesconnected contact points in said chambers, an insulating conduit connecting each of said gas-filled spaces to said compressed gas source, each breaking chamber being provided with a feeding valve between the gas-filled space in the chamber and the insulating conduit, said feeding valves being open during normal operation, thereby providing free communication between the gas-filled spaces in different breaking chambers, but arranged to close during a breaking process when the pressure in said spaces exceeds a certain value.

2. High voltage circuit breaker according to claim 1, in which each feeding valve is arranged so that, when it is closed, it remains closed for a predetermined period.

3. High voltage circuit breaker according to claim I, in which each breaking chamber is provided with an exhaust valve in communication with the gas-filled space and arranged to open when the pressure in the chamber exceeds a certain value.

4.]High voltage circuit breaker according to claim 3, in which when, after a breaking process, the pressure in the breaking chamber decreases, the feeding valve opens before the exhaust valve closes.

5. High voltage circuit breaker according to claim 1, in which each breaking chamber has its longitudinal axis directed upwardly, and in which the movable contact of each contact point is moved downwardly when the breaker opens.

6. High voltage circuit breaker according to claim 5, in which the breaking chambers are arranged in pairs in a V-formation'.

7. High voltage circuit breaker according to claim 5, in which the gas-filled spaces are situated at the upper end of the respective breaking chambers, and in which the compressed gas connection to said spaces comprises an insulating conduit in each breaking chamber.

8. High voltage circuit breaker according to claim 5, in which the compressed gas connection to each gas-filled space comprises an external porcelain tube.

9.'High voltage circuit breaker according to claim 1, in which the compressed gas source comprises a compressor feeding several poles and from which the compressed gas is led to the breaking chambers through an air-drying means, a storage tank and a reducing valve. 

2. High voltage circuit breaker according to claim 1, in which each feeding valve is arranged so that, when it is closed, it remains closed for a predetermined period.
 3. High voltage circuit breaker according to claim 1, in which each breaking chamber is provided with an exhaust valve in communication with the gas-filled space and arranged to open when the pressure in the chamber exceeds a certain value.
 4. High voltage circuit breaker according to claim 3, in which when, after a breaking process, the pressure in the breaking chamber decreases, the feeding valve opens before the exhaust valve closes.
 5. High voltage circuit breaker according to claim 1, in which each breaking chamber has its longitudinal axis directed upwardly, and in which the movable contact of each contact point is moved downwardly when the breaker opens.
 6. High voltage circuit breaker according to claim 5, in which the breaking chambers are arranged in pairs in a V-formation.
 7. High voltage circuit breaker according to claim 5, in which the gas-filled spaces are situated at the upper end of the respective breaking chambers, and in which the compressed gas connection to said spaces comprises an insulating conduit in each breaking chamber.
 8. High voltage circuit breaker according to claim 5, in which the compressed gas connection to each gas-filled space comprises an external porcelain tube.
 9. High voltage circuit breaker according to claim 1, in which the compressed gas source comprises a compressor feeding several poles and from which the compressed gas is led to the breaking chambers through an air-drying means, a storage tank and a reducing valve. 